This invention relates to a load-bearing structural member. The structural member includes one or more strength-reinforcing, tensioned steel straps adapted for transferring an intermediate lateral load acting on the member to its supported ends. The invention is applicable to standard light-gauge steel C-channels, U-channels, Z-purlins, I-beams, and girts, square tubing, and light-gauge prefabricated building sections, such as floor trusses, stud or curtain walls, and roof panels. The invention provides a lightweight structural member with an extended span reach, and which is less costly and more functional than existing structures of equivalent strength and span.
A principle object of the invention is to create a maximum supporting reaction force at a predetermined location between the ends of the structural member in a manner that will not significantly increase the weight and/or cost of the member. The invention will double the span of the structural member without reducing its load-bearing capacity. For example, a standard 24 foot beam has a maximum supporting reaction force at its supported ends and a minimum supporting reaction force at its center point 12 feet from either end. Longer beams have less strength at the center point, and must therefore be made of a heavier gauge steel or must include separately attached reinforcing structure which can substantially increase the overall weight and cost of the beam. The present invention adds low cost, lightweight reaction support at the center point of the beam, thereby shifting the area of less strength to respective mid-points between the center and ends of the beam.
Attempts have been made in the past to strengthen conventional beams using or more steel cable tendons attached to opposite ends of the beam in tension, and forced downwardly and attached at intermediate points of the beam. Cable tendons, however, are costly and generally too elastic to maintain proper tension over time. For example, for every 1/50th of an inch of relaxing tension on a steel cable under 2500 lbs. of tension, residual tension in the cable is reduced by 100 lbs. To control elongation, the cables are typically pretensioned and imbedded in relatively heavy cement-type material and held rigid the full length of the beam. This is not an option with light-gauge structural members.